In a polysilicon thin film transistor, polysilicon material is used to form an active region. The polysilicon in the active region may be formed from an amorphous silicon layer, and specifically, an amorphous silicon layer may be first formed and then be irradiated with laser to be melted, the melted silicon turns into polysilicon after being solidified again, and such a process is referred to as “laser annealing” .
Grain size, growth direction, distribution and the like of the polysilicon in the active region have an important influence on performance of a thin film transistor, and these parameters are all related to temperature distribution (temperature gradient) in the laser annealing. However, in an existing laser annealing process, annealing temperature can be controlled simply by adjusting laser power only, it is very difficult to form a certain temperature gradient, and thus, performance of the obtained polysilicon active region cannot be controlled.